E.C. Marchant, Commentary on Thucydides Book 1

[6] 14. καὶ ἰδίᾳ κτλ.—and for the Athenians themselves and with a view to (the interests of) the allies in general it would be beneficial. The position of the allies would be secure in the general council if Athens was strong. (This passage has been much discussed: (1) Classen takes τοῖς πολίταις with ἐς τοὺς π. ξυμμάχους also, and understands, ‘would be of more advantage to the Athenians (both) separately and with regard to their relations with the allies.’ But it is rightly objected that the advantage of the fortification cannot be limited to the Athenians, who want to prove that it is good for the allies too (cf. c. 91. 4 τὰ κοινά). Steup deletes ἄμεινον εἶναι, and is thus able to transl. the καὶ ἰδίᾳ κτλ. both for the A. themselves and for the allies. But there is no decisive objection to the text as it stands. It is true that we expect ίδίᾳ τε or καί (‘both’) ἰδίᾳ; cf. τά τε σφίσιν αὐτοῖς ... καἱ τὰ κοινά: but the omission and the unusual ἐς τούς instead of dative serve to make the allusion to ‘the allies’ a climax; καί=‘and in fact.’）

15. ὠφελιμώτερον ἔσεσθαι—the argument is that this, like the earlier actions of Athens, was done ἐπ᾽ ὠφελίᾳ, not only for Athens but for the Greek allies in general. Cf. c. 73. 2.